JP2575669B2 - Graphite free-cutting cast steel - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a graphite free-cutting cast steel, and more particularly to a graphite free-cutting cast steel having excellent machinability and mechanical properties as cast.

(Prior art and its problems) Conventionally, graphite steel or graphite cast steel in which spheroidal graphite is precipitated in steel or a casting in order to facilitate plastic working, cutting work and the like has been known. As a method of depositing graphite,
Graphite steel can be subjected to graphitization heat treatment to precipitate graphite. Therefore, it is difficult to achieve the intended purpose by heat treatment. However, if inoculation treatment of Mg, Ca, etc. is performed at the time of smelting, spheroidal graphite can be distributed in the casting as it is.

Such a conventional graphite cast steel is one in which graphite is distributed in the casting without performing a graphitization heat treatment by inoculating Mg, Ca, etc. at the time of melting, but the distribution of spheroidal graphite is not uniform, Moreover, since the precipitated graphite has a large particle size, satisfactory properties such as machinability have not yet been obtained.

The present invention has been made in order to solve such a problem, and the machinability and mechanical properties are further improved by uniformly distributing finer spheroidal graphite in the casting in a cast state than conventional graphite cast steel. It is an object of the present invention to provide a graphite free-cutting cast steel having improved steel.

(Means and Actions for Solving the Problems) In order to achieve the above object, the present inventors have conducted various studies on additional elements to be inoculated at the time of smelting.
It has been found that the addition of a rare earth element (REM) from No. to Lu with an atomic number of 71 allows fine spherical graphite to be densely and uniformly distributed in the casting as it is. The present invention is based on such a novel finding, and according to the first present invention, C: 0.45 to 2.0%, Si: 1.0 to 3.2%, REM: 0.01 to 1.0% by weight.
%, With the balance being Fe and impurities.

According to the second to fourth aspects of the present invention, the composition of the graphite free-cutting steel according to the first aspect of the present invention further includes Ni: 1.5% or less, Cu: 1.5% or less, Ca: 0.4% or less, and Mg: Provided is a free-cut graphite cast steel containing one or more selected from 0.4% or less, and / or one or two selected from Pb: 0.4% or less and Bi: 0.4 or less.

As REM, La of atomic number 57 to Lu of atomic number 71
One or more rare earth elements described above, and among these rare earth elements, La and Ce are suitably selected.

 Next, the reasons for limiting the component range of the present invention will be described.

C: 0.45-2.0% Element indispensable for graphite formation, lower limit 0.45% by weight
Below, the precipitation amount of spheroidal graphite is small, the effect of improving machinability by graphite is remarkably small, and if it exceeds the upper limit of 2.0%, reticulated graphite is precipitated. Characteristic deteriorates.

Si: 1.0 to 3.2% Si has an effect of accelerating the deposition of graphite, and the lower limit is 1.0.
% Or less, the effect is small and the amount of graphite deposition is small. On the other hand, when it exceeds 3.2% of the upper limit, the hardness of the cast steel increases, and the ductility deteriorates remarkably.

REM: 0.01 to 1.0% REM promotes graphite precipitation, and the REM-free material hardly causes graphite precipitation. If the lower limit is 0.01% or less, the effect of depositing graphite is small, and if it exceeds 1.0% of the upper limit, the casting is significantly shrunk and cracks may occur.

Ni, Cu: 1.5% or less These elements have the effect of miniaturizing the precipitated graphite, but the effect is saturated at 1.5%, and the addition of more than that does not improve the miniaturization of graphite.

Ca, Mg: 0.4% or less When these elements are added together with REM, they help the graphite precipitation accelerating action of REM, and have the same graphite refining effect as Ni, Cu described above. However, the effect is saturated and the miniaturization is not improved.

In addition, Ni, Cu, Ca, and Mg are each added alone or in combination within the above-described component ranges. _{Pb, Bi: 0.4% or less} Both Pb and Bi are machinability improving elements, but if the content exceeds the upper limit, the graphite shape becomes non-spherical and mechanical properties are significantly impaired.

The elements that inhibit the precipitation of graphite include Al, Ti, Mn, P,
S, Cr, Mo, W, V, Nb, etc., these impurity elements Mn: 0.3
% Or less, P: 0.015% or less, S: 0.010% or less, Cr: 0.10% or less, Mo: 0.01% or less, W: 0.01% or less, v: 0.01% or less, Nb:
It is preferable to regulate the content to 0.01% or less.

(Example) Hereinafter, an example of the present invention will be described.

Table 1 shows the chemical composition of the cast steel of the present invention and the comparative steel (cast steel), the results of machinability tests thereof, and the like. The test materials of Test No. 1 to Test No. 5 are the cast steels of the present invention, and Test No. A to Test No.
The test material of No. G is a comparative steel (cast steel). The test material for test No. A is JIS S30C equivalent material, the test material for test No. B is JIS S50C equivalent material, and the test material for test No. C is JIS S50CL equivalent material. Test N
o.1 to Test No.15 and Test No.D to Test No.G were prepared by dissolving the raw materials of the components shown in Table 1 in a 50 kg induction furnace, and adjusting the components to have a diameter of 35 mm and a length of 80 mm. , And subjected to a cutting test and a tensile test without heat treatment. Test No.1
Mish metal was added as a REM to each test material of Test No. 15 to Test No. 15. For the test materials of Test Nos. A to C, test pieces of the same shape as above were cut out from a rolled material obtained by melting the raw materials of the components shown in Table 1, and held at 850 ° C. for 2 hours, followed by air-cooling heat treatment. gave.

In the cutting test, a round bar with the above shape was cut to a length of 50 mm, and a high-speed drill (SKH51) was used as a cutting tool.
The relationship between the tool life and cutting speed of each test piece was determined, and test No.
Table 1 shows the ratio of the cutting speed of each test material at a tool life of 1000 mm to the cutting speed of the reference test material at a tool life of 1000 mm as a cutting efficiency.

As shown in Table 1, the comparative steels or comparative cast steels shown in Test Nos. A to F have no or very little graphite precipitation, and the cast steels shown in Test Nos. The cutting efficiency is remarkably small compared to the material.

The amount of Si was fixed to a value close to 2.4%, the amount of REM was fixed to a value near 0.1%, and both were fixed within the specified value range of the present invention. (Test N
Comparing o.1 to 3), graphite density, average graphite particle diameter and cutting efficiency, all showed that the best results were obtained when the C content was around 1.0%. μm fine graphite is distributed at a density of 2230 pieces / mm ² , and the cutting efficiency is also tested.
6.2 times higher than oD standard test material.

When the C content is fixed at around 1.0% where the results of cutting efficiency and the like are good, and the Si content is changed from the upper limit value near the specified value range of the present invention to the lower limit value (Test Nos. 2, 4, and 5) And Si, the best cutting efficiency can be obtained at a substantially intermediate value in the specified value range.
Also, fix the C content and the Si content to approximately the center value of the specified value range,
When the amount of M was changed from a value near the upper limit of the specified range to a value near the lower limit (Test Nos. 2, 6, and 7), the graphite density increased with the increase in the amount of REM, but the average graphite particle size was 0.1% of the amount of REM. %, And the REM minimizes the cutting efficiency and the average graphite particle size.
The highest value is shown at around 0.1% of the amount. The test material for test No.F is R
Although no EM is added, the graphite density is low and graphite is not uniformly deposited.

The test material of test No.8 was Ni
However, the graphite can be refined by the graphite refining action of Ni, and the graphite density can be further increased.
FIG. 1 is a micrograph of the metal structure of the test material of Test No. 8, in which fine graphite is uniformly distributed.
The comparative material of Test No. G has improved cutting efficiency by precipitating graphite by Mg inoculation, but has a low graphite density and a large graphite particle size (see FIG. 2).

The refining action of graphite particles can be used instead of or together with Ni
Similar effects can be obtained by adding Cu, Ca and Mg (Test N
o.9,10). However, although the test material of test No. 9 improved the cutting efficiency, the tensile strength was slightly reduced, and the test material of test No. 10 was inferior in cutting efficiency and tensile strength compared to test No. 8, but the cutting efficiency was lower. Is superior to any comparative steel (cast steel).

When Pb and / or Bi are added to the test material to which the amounts of C, Si, and REM within the range specified by the present invention are added, the machinability is further improved. The diameter increases and the graphite density decreases (Test Nos. 11 and 12). Further, Ni, Cu, Ca, and Mg are added to the test material to which the amounts of C, Si, and REM within the range specified by the present invention are added. Inoculate one or two species,
Furthermore, by inoculating one or two types of Pb and Bi,
The particle size of the precipitated graphite becomes finer, and the same cutting efficiency as the test material of Test No. 8 can be obtained.

In each of the cast steels of the present invention of Test Nos. 1 to 15, a large amount of fine graphite was precipitated compared with the comparative steel (cast steel), and the cutting efficiency was remarkably improved. Although many were inferior to the test materials, they showed sufficiently satisfactory values as compared with Test Nos. A to C.

(Effects of the Invention) As described in detail above, the graphite free-cutting steel of the present invention contains C and Si in a regulated value range, and inoculates 0.01 to 1.0% of REM into this, and further, Ni: One or more selected from 1.5% or less, Cu: 1.5% or less, Ca: 0.4% or less and Mg; 0.4% or less, and / or one selected from Pb: 0.4% or less and Bi: 0.4% or less Alternatively, by inoculating two types, a large number of fine spheroidal graphites can be precipitated in a casting, and an excellent effect of improving machinability and mechanical properties as cast can be obtained.

[Brief description of the drawings]

FIG. 1 is a micrograph of the metal structure of the cast steel of the present invention of Test No. 8 shown in Table 1, and FIG. 2 is a micrograph of the metal structure of the comparative cast steel of Test No. G shown in Table 1.

Claims (4)

(57) [Claims] (1) C: 0.45 to 2.0% by weight, Si: 1.0 to 3.2% by weight,
REM: Graphite free-cutting cast steel with excellent machinability as cast, containing 0.01 to 1.0%, the balance being Fe and impurities. 2. C: 0.45 to 2.0% by weight, Si: 1.0 to 3.2% by weight,
REM: 0.01-1.0%, Ni: 1.5% or less, Cu: 1.5% or less, and Ca: 0.
Graphite free-cutting cast steel with excellent machinability as cast, containing one or more selected from 4% or less and Mg: 0.4% or less, with the balance being Fe and impurities. 3. C: 0.45 to 2.0% by weight, Si: 1.0 to 3.2% by weight,
REM: 0.01 to 1.0%, Pb: 0.4% or less, Bi: 0.4% or less, containing one or two selected from the group consisting of Fe and impurities, with excellent as-cast machinability and excellent machinability . (4) C: 0.45 to 2.0%, Si: 1.0 to 3.2% by weight%,
REM: 0.01-1.0%, Ni: 1.5% or less, Cu: 1.5% or less, and Ca: 0.
Casting containing one or two or more selected from 4% or less and Mg: 0.4% or less, and one or two selected from Pb: 0.4% or less and Bi: 0.4% or less, with the balance being Fe and impurities Graphite free-cutting cast steel with excellent machinability as it is.